Usually, after formation of diastereomeric salts in a resolution procedure, one of the pair will preferentially crystallize in a somewhat optically impure form. Purification of this salt frequently requires repeated recrystallizations involving large volumes of solvents and loss of time and of yield.
Now with the present invention a single operation, stirring the impure salt with the desired isomer, provides the desired salt in about 90% yield and 99% optical purity. The same principle is applicable to the separation of other types of isomers and simple homologs and analogs.